We propose extension and development of our past research on the acidity of hydrocarbons to the determination of quantitative measures of acidity of a variety of other carbon acids. Carbanions are among the most important intermediates and proton transfer is one of the most important reactions in organic an biochemical processes. Our goal in this study is fundamental knowledge of the effect of structural changes on carbanion stability and of the role of solvent and ion-pairs in proton transfer reaction mechanisms. Expermental methods include spectroscopic determination of equilibrium acidities and base-catalyzed hydrogen isotope exchange kinetics of various carbon acids: aromatic hydrocarbons, saturated and unsaturated alkanes and cycloalkanes, sulfur-, phosphorus-, silicon- and other substituted systems. The studies of reaction mechanism include substitutent effects, primary and secondary isotope effects and Bronsted correlations. A complemetary theoretical study includes ab initio SCF calculations of suitable model systems.